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ENH: add to_grayscale() method to color maps #3589

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ENH: add to_grayscale() method to color maps #3589

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12 changes: 12 additions & 0 deletions lib/matplotlib/colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -665,6 +665,18 @@ def is_gray(self):
return (np.alltrue(self._lut[:, 0] == self._lut[:, 1]) and
np.alltrue(self._lut[:, 0] == self._lut[:, 2]))

def to_grayscale(self):
"""Return a grayscale version of the colormap"""
colors = self(np.arange(self.N))

# convert RGBA to perceived greyscale luminance
# cf. http://alienryderflex.com/hsp.html
RGB_weight = [0.299, 0.587, 0.114]
luminance = np.sqrt(np.dot(colors[:, :3] ** 2, RGB_weight))
colors[:, :3] = luminance[:, np.newaxis]

return self.from_list(self.name + "_gray", colors, self.N)


class LinearSegmentedColormap(Colormap):
"""Colormap objects based on lookup tables using linear segments.
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